The transitions are not available, but you can create transition-like effects on the scene timeline. For example, if you want your scene to fade to black, add a black square on top of the scene, set its opacity to 0% and on the last 0.5 second of the scene make it transition from 0% to 100% opacity. Other effects like slide-in/out, fade-to-white, etc can be created in a similar way.